Cosmic Conundrum Hits Close to Home

Dec. 12, 2008 -- By the time cosmic rays hit Earth, they have journeyed through so many magnetic fields and other perturbations that they arrive nearly uniformly from all directions.

So when a detector in New Mexico began registering streams of charged particles coming from the general direction of the Orion nebula and about 500 light-years from Earth -- a neighbor by astronomical measures -- scientists took note.

"I can't tell you what it is, but I can tell you what it isn't," said University of Maryland physicist Jordan Goodman, "It isn't a statistical fluctuation in our data. It's not an error."

Scientists aren't sure what causes cosmic rays, which are charged particles, namely protons and electrons, moving at high speeds due to unknown events. The list of candidates includes supernova explosions and quasars.

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A local source of cosmic rays is one explanation for the finding made by Goodman and his colleagues, though what that could be is pure conjecture.

Another theory is that the rays originate from afar, but are being funneled toward Earth due to a magnetic field from an object such as Geminga, a relatively young pulsating star that is surrounded by clouds of molecular gas. Geminga radiates brilliantly in high-energy gamma rays.

"If Geminga is the source, it isn't clear that we would see it," Goodman said. "The magnetic fields would have to be aligned in some way" relative to Earth.

The finding was the second in less than a month that uncovered unusual evidence of cosmic rays.

Scientists using a detector on a balloon-borne experiment above Antarctica found more cosmic ray electrons than expected and suggested dark matter may be responsible, since the energy signals match what physicists believe would result when dark matter is annihilated.